This present invention relates intelligent pigs used in oil and gas pipelines to diagnose defects in pipeline walls.
It is common practice to insert an intelligent pig into a pipeline and move the pig through the pipeline as an in-line inspection tool. The pig usually has urethane cups located in a front towing portion that seal with the pipeline wall and tow the intelligent portion of the pig through the pipeline by either gas or oil (fluids) in the pipeline pushing the cups as this product flows in the pipeline. The intelligent portion of the pig collects data concerning defects in the pipeline wall as it is towed through the pipeline. The information collected on these anomalies comprises, for example, the location, size and shape of cracks, pits, dents and corrosion in the pipeline wall. This information is stored in the pig and later retrieved from the pig when it is removed from the pipeline. This information can then be analyzed and the pipeline repaired as needed.
It is known for the intelligent pig in-line inspection tool to measure the magnetic flux leakage associated with defects in pipeline walls. The tool accomplishes this by magnetizing the pipeline wall and using sensors to measure the leakage field generated by any defects. The magnetic field is usually constant when no defects in the wall are present and as a result constant leakage is detected. When there is a defect in the wall, the magnetic field induced by the pig in the pipeline wall becomes more concentrated and increased leakage of magnetic fields develop which are measured to obtain information about the defect in the pipeline wall.
U.S. Pat. No. 6,847,207 issued Jan. 25, 2005 discloses an inspection tool that measures magnetic flux leakage in the pipeline wall caused by anomalies in the pipeline wall. Magnetic flux leakage measuring technology relies on hall effect sensors to measure the magnitude of the defect that causes the flux leakage to occur. The location of the defect in the pipe wall, that is closer to the inside diameter (ID) or outside diameter (OD) cannot be determined from magnetic flux leakage measuring technology due to the physics of the magnetic flux leakage paths around the defect. U.S. Pat. No. 6,847,207 teaches that ID/OD discrimination is accomplished by using an eddy current pulser coil and an eddy current detection coil, or a two coil pair, to provide a signal used to indicate whether a detected flux leakage anomaly is in the interior surface of the pipeline wall. However, the use of two coils, a pulser coil and a sensor coil, increases the size requirement of the sensor body and the associated circuitry required to pulse one coil and read the other coil.